Physical vapor deposition is extensively used to apply ceramic thermal barrier coatings on turbine airfoils by electron beam evaporation. Extensive work has been done to design coating processes and associated fixturing to apply a uniform coating on a variety of airfoil sizes and shapes. Physical vapor deposition is a line of sight coating process. Substrates to be coated need to be manipulated in the vapor to achieve uniform coverage. Sections of the substrate that do not require a coating need to be masked adequately.
U.S. Pat. No. 5,997,947 discloses a modular, rotisserie type coating fixture for use in electronic beam physical vapor deposition (EBPVD) coating processes. Tooling fixtures used in the EBPVD coating process generally include a support structure and means to couple the support structure and allow it to be rotated about a first axis. The tooling fixture further includes a cassette means within the support structure for holding one or more workpieces to be coated in place. The cassette means are joined to the support structure by spindles which allow the cassette means to rotate about a second axis substantially parallel to the first axis and thereby allow each workpiece being coated to rotate about its longitudinal axis. The cassette means support each workpiece so that surfaces of the airfoil to be coated are maintained substantially parallel to the coating source. However, loading of the workpieces within each of the cassettes can be time consuming. Furthermore, the cage-like structures of the cassettes involve complicated construction.
U.S. Pat. No. 7,837,843 discloses a rotisserie type tooling fixture assembly for use in a physical vapor deposition coating operation which comprises a cylindrical type support structure comprising a circular base member, a circular top member opposite the circular base member, and a plurality of structural members joining the top member to said base member. The workpieces are arranged in a plurality of panel members aligned in a staggered vertical direction around the outer periphery of said support structure forming the cylinder-like structure. While this tooling fixture orients the workpieces to improve the throughput of workpieces to be coated, there is no resolution of the issues and problems associated with workpiece masking.
While most prior art tooling fixtures all hold multiple workpieces or airfoils at optimum angles, there continues to be a need in the art for coating fixtures for use in a physical vapor deposition coating operation which allow for improved loading of workpieces and masking operations which promote and advance the production of high quality coatings. What is needed therefore is improved tooling and fixtures for coating operations that improve the workpiece loading and masking operations. Further, such improved coating fixtures and tooling should be reusable and relatively inexpensive to fabricate.